And where was Dick Worden, my great great grandfather, at the time? Was he one of the marchers in Washington D.C.?

Alas, no.

After being invalided out shortly after Vicksburg in 1863, he had reenlisted early in the next year and went back to his old Company G of the 24th Iowa Infantry Regiment, then part of General Sheridan's Army of the Shenandoah in Virginia, which was in Georgia when the Grand Review took place.

*The men from General Sherman's Army of Georgia, 60,000 strong, traveled the same route the next day.
**Either Savannah or Augusta.